Application of advanced oxidation processes and toxicity assessment of transformation products

Insights on the current status of occurrence and removal of antibiotics in wastewater by advanced oxidation processes

Antibiotics are considered as the significant group of pharmaceuticals which causes a serious hazard to the environment and human health in recent years. Due to the inefficient treatment technologies, conventional wastewater treatment plants (WWTPs) are unable to remove many antibiotics from wastewater. This review encapsulates the current status of antibiotics occurrence in influent and effluent of WWTPs globally. Specifically, β-lactams, fluoroquinolones, macrolides, sulfonamides, tetracyclines classes of antibiotics are found to be high in wastewater. An overview of physicochemical properties, generation classifications of antibiotics, and different advanced oxidation processes (AOPs) available for the removal of emerging pollutants are presented. Besides, the removal efficiency of diverse antibiotics by various AOPs are discussed. The combination such as UV/H₂O₂, UV/H₂O₂/Fe²⁺ and ozonation are reported for maximum removal of antibiotics. However, when compared to simulated wastewater, limitations are persisted for the removal of antibiotics in real wastewater, owing to its difficulty in assessing and observing the compound under mixed nature. AOPs assisted degradation mechanism for ciprofloxacin antibiotic in wastewater is presented and the necessity of research on antibiotic removal is highlighted.

Pharmaceutically active compounds in aqueous environment: A status, toxicity and insights of remediation

Pharmaceutically active compounds (PhACs) have pernicious effects on all kinds of life forms because of their toxicological effects and are found profoundly in various wastewater treatment plant influents, hospital effluents, and surface waters. The concentrations of different pharmaceuticals were found in alarmingly high concentrations in various parts of the globe, and it was also observed that the concentration of PhACs present in the water could be eventually related to the socio-economic conditions and climate of the region. Drinking water equivalent limit for each PhAC has been calculated and compared with the occurrence data from various continents. Since these compounds are recalcitrant towards conventional treatment methods, while advanced oxidation processes (AOPs) have shown better efficiency in degrading these PhACs. The performance of the AOPs have been evaluated based on percentage removal, time, and electrical energy consumed to degrade different classes of PhACs. Ozone based AOPs were found to be favorable because of their low treatment time, low cost, and high efficiency. However, complete degradation cannot be achieved by these processes, and various transformation products are formed, which may be more toxic than the parent compounds. The various transformation products formed from various PhACs during treatment have been highlighted. Significant stress has been given on the role of various process parameters, water matrix, oxidizing radicals, and the mechanism of degradation. Presence of organic compounds, nitrate, and phosphate usually hinders the degradation process, while chlorine and sulfate showed a positive effect. The role of individual oxidizing radicals, interfering ions, and pH demonstrated dissimilar effects on different groups of PhACs.

Fabrication of a double-helical photocatalytic module for disinfection and antibiotics degradation

A double-helical photocatalytic module was fabricated via an annealing process following an anodic oxidation procedure, and installed into a commercial UV sterilizer to structure continuous-flow photocatalytic device. Benefiting from the superior mass transfer of double-helical structure to common flat plate or corrugated plate, as well as the improved adhesion between Ti support and TiO₂ layer, the photocatalytic device displayed potential in practical disinfection and degradation of organics. During photocatalytic disinfection process with 21 mJ/cm² of UV dose, the concentration of Escherichia coli decreased from 1.71 × 10⁷  CFU/L (typical for municipal wastewater) in influent to 2,720 CFU/L in effluent water, which met the wastewater discharged standard of China. Escherichia coli reactivation ratio for the photocatalytic device was only one-tenth of that for UV sterilizer. Furthermore, taking phenol, bisphenol A, and four antibiotics as targets, the device was demonstrated to promote the degradation of photodegradable pollutants via photocatalysis. These results highlight a feasibility of photocatalytic technology as a supporting role in practical wastewater treatment. PRACTITIONER POINTS: TiO₂ nanotube array was embedded in the surface of double-helical Ti support to avoid detachment. This double-helical photocatalytic module was installed into a commercial UV sterilizer to structure a continuous-flow device. The continuous-flow device was effective in sterilizing bacteria and decomposing photodegradable organic pollutants in wastewater. Improving the performance of UV technology was proposed as a feasible approach for the practical application of photocatalysis.

Removal of chloramphenicol in aqueous solutions by modified humic acid loaded with nanoscale zero-valent iron particles

As a natural organic carbon skeleton, humic acid (HA) was loaded with nanoscale zero-valent iron (nZVI) Particles to remove chloramphenicol (CAP) from aqueous solution. The pore morphology and structure, the type, the distribution and valence state of element, and the class of functional groups on the surface of the material were shown by SEM/EDS, XPS, BET and FTIR. When the load ratio of nZVI on HA was 1:30, the iron content in the material was minimized, the specific gravity of the economic material-HA was increased, and the removal efficiency of CAP was 80.0% or higher. In addition, the mass ratio of nZVI on HA, the dosage of nZVI/HA-30, the initial pH and CAP concentration of the solution, these four general factors, played an important role in the efficiency and equilibrium time of the CAP removal. The removal efficiency of CAP by nZVI/HA-30 was 84.2% when the dosage was 1.0 g (100 mL)^-1, the initial concentration of CAP was 30 mg L^-1 and the pH was 3. The reaction pathway and removal mechanism of ZVI/HA-30 were studied by the concentration of total and ferrous iron ions in the solution, UV-Vis and MS. The CAP was continuously denitrified and dechlorinated, decomposed into easily degradable substances by nZVI particles supported on HA, which was consistent with the first-order kinetic model within 5 min. This newly synthesized material was economical and efficient, easy to store, effectively prevented agglomeration and passivation of nZVI, and had a good application prospect for removing contaminants from water.

A review on Fenton process for organic wastewater treatment based on optimization perspective

Water pollution caused by organic wastewater has become a serious concern worldwide. Fenton oxidation process is one of the most effective and suitable methods for the abatement of organic pollutants. However, the process has three obvious shortcomings: the narrow working pH range, the high costs and risks associated with handling, transportation and storage of reagents (H₂O₂ and catalyst), the significant iron sludge related second pollution. In order to overcome these shortcomings, various optimized Fenton processes have been widely studied. Therefore, a summary of the study status of Fenton optimization processes is necessary to develop a novel and high efficiency organic wastewater treatment method. Based on the optimization perspective, taking shortcomings of Fenton process as a breakthrough, the fundamentals, advantages and disadvantages of single Fenton optimization processes (heterogeneous Fenton, photo-Fenton and electro-Fenton) for organic wastewater treatment were reviewed and the corresponding reaction mechanism diagrams were drawn in this paper. Then, the feasibility and application of the coupled Fenton optimization processes (photoelectro-Fenton, heterogeneous electro-Fenton, heterogeneous photoelectro-Fenton, three-dimensional electro-Fenton) for organic wastewater treatment were discussed in depth. Additionally, the effect of some important operation parameters (pH and catalyst, H₂O₂, organic pollutants concentration) on the degradation efficiency of organic pollutants was studied to provide guidance for the optimization of operation parameters. Finally, the possible future research directions for optimized Fenton processes were given. The review aims to assist researchers and engineers to gain fundamental understandings and critical view of Fenton process and its optimization processes, and hopefully with the knowledge it could bring new opportunities for the optimization and future development of Fenton process.

Investigation of Microstructure and Photocatalytic Performance of a Modified Zeolite Supported Nanocrystal TiO2 Composite

A modified zeolite/TiO2 composite (MZTC) was prepared through a method of saturated infiltration and synthesis in situ. The crystalline phase, micromorphology, elementary composition, specific surface area, pore size distribution, chemical bond and band gap variation of the products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), BET specific surface area and pore size distribution analysis (BET), Fourier transform infrared spectroscopy (FTIR) and UV–vis diffuse reflectance spectroscopy (UV-vis DRS), respectively. The microscopic characterization results showed that TiO2 was homogeneously dispersed in the structure of zeolite at the nanoscale range, and a strong chemical bond was established between TiO2 and zeolite. The photocatalytic performance of MZTC was evaluated by studying the degradation rate of methylene blue (MB) dye in aqueous solution under UV-light irradiation. The results of the degradation experiment showed that the MB degradation rate of MZTC-2.5 was the highest, reaching 93.6%, which was 2.4 times higher than hydrolysis TiO2 powder (HTOP) containing the same mass of pure TiO2. The MB degradation rate of MZTC-2.5 still maintained 86.5% after five tests, suggesting the excellent recyclability of MZTC-2.5. The possible mechanism of MB degradation was also discussed.

Controlled Microwave-Assisted Synthesis of the 2D-BiOCl/2D-g-C3N4 Heterostructure for the Degradation of Amine-Based Pharmaceuticals under Solar Light Illumination

Designing efficient 2D-bismuth oxychloride (BiOCl)/2D-g-C₃N₄ heterojunction photocatalysts by the microwave-assisted method was studied in this work using different amounts of BiOCl plates coupled with g-C₃N₄ nanosheets. The effects of coupling the 2D structure of g-C₃N₄ with the 2D structure of BiOCl were systematically examined by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, X-ray diffraction, photoluminescence (PL), lifetime decay measurement, surface charges of the samples at various pH conditions, and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The prepared photocatalysts were used for the degradation of amine-based pharmaceuticals, and nizatidine was used as a model pollutant to evaluate the photocatalytic activity. The UV-vis DRS and other optical properties indicated the major effect of coupling of BiOCl with g-C₃N₄ into a 2D/2D structure. The results showed a narrowing in the band gap energy of the composite form, whereas the PL and lifetime analysis showed greater inhibition of the electron-hole recombination process and slightly longer charge carrier lifetime. Accordingly, the BiOCl/g-C₃N₄ composite samples exhibited an enhancement in the photocatalytic performance, specifically for the 10% BiOCl/g-C₃N₄ sample. Moreover, the zeta potential of this sample at different pH values was evaluated to determine the isoelectric point of the synthesized composite material. Consequently, the pH was adjusted to match the isoelectric point of the complex materials, which further enhanced the activity. Further degradation of pharmaceuticals was studied under solar light irradiation, and 96% degradation was achieved within 30 min.

Reusability and photocatalytic activity of bismuth-TiO2 nanocomposites for industrial wastewater treatment

In this study, bismuth-TiO₂ nanotube (Bi-TNT) composites were used for the treatment of industrial wastewater. Bi-TNT were synthesized using two- and one-step anodization methods. The obtained composites were analyzed using X-ray diffraction, field emission scanning electron microscopy, UV-visible diffuse reflectance spectroscopy, Energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. For the two-step Bi-TNT composites, we investigated the effect of different Bi deposition times, Bi concentrations, and Bi deposition voltages on photodegradation efficiency. For the one-step Bi-TNT composites, we investigated the effect of different anodization voltages, anodization times, and Bi concentrations. Initially, the optimal synthesis conditions for two- and one-step Bi-TNT catalysts were identified and then these optimized conditions were used for industrial wastewater treatment that was collected from Banwol Sihwa Industrial Complex Republic of Korea. The Bi-TNT two- and one-step composites showed 2.0 and 2.5 times higher photocatalytic activity, respectively, for industrial wastewater treatment than that of TNT in visible-light. Recycling of Bi-TNT composites showed that the one-step composite method was more efficient and stable than the two-step method because Bi coupling and nanotube formation simultaneously occurred.

Mechanisms of Methylparaben Adsorption onto Activated Carbons: Removal Tests Supported by a Calorimetric Study of the Adsorbent⁻Adsorbate Interactions

: In this study, the mechanisms of methylparaben adsorption onto activated carbon (AC) are elucidated starting from equilibrium and thermodynamic data. Adsorption tests are carried out on three ACs with different surface chemistry, in different pH and ionic strength aqueous solutions. Experimental results show that the methylparaben adsorption capacity is slightly affected by pH changes, while it is significantly reduced in the presence of high ionic strength. In particular, methylparaben adsorption is directly dependent on the micropore volume of the ACs and the π- stacking interactions, the latter representing the main interaction mechanism of methylparaben adsorption from liquid phase. The equilibrium adsorption data are complemented with novel calorimetric data that allow calculation of the enthalpy change associated with the interactions between solvent-adsorbent, adsorbent-adsorbate and the contribution of the ester functional group (in the methylparaben structure) to the adsorbate⁻adsorbent interactions, in different pH and ionic strength conditions. It was determined that the interaction enthalpy of methylparaben-AC in water increases (absolute value) slightly with the basicity of the activated carbons, due to the formation of interactions with π- electrons and basic functional groups of ACs. The contribution of the ester group to the adsorbate-adsorbent interactions occurs only in the presence of phenol groups on AC by the formation of Brønsted⁻Lowry acid⁻base interactions.

The construction of accelerated catalytic Fenton reaction based on Pd/MIL-101(Cr) and H2

A novel catalytic Fenton system based on H₂ and the solid catalyst Pd/MIL-101(Cr) (MHACF-MIL-101(Cr)) was developed at normal temperature and pressure. In this system, the reduction process of Fe^III back to Fe^II was accelerated significantly.